The overall goal of this early phase, multi-site clinical trial is to validate and demonstrate the clinical utility of a consensus protocol for dynamic susceptibility contrast (DSC) MRI. Contrast-enhanced MRI is the clinical imaging standard for guiding nearly all aspects of brain tumor management. Its inability to reliably monitor treatment response and differentiate tumor recurrence from posttreatment radiation effect (PTRE) often forces clinicians to rely upon surgical biopsy for definitive diagnosis, which increases cost, morbidity, and resource utilization. A definitive imaging-based diagnosis that obviates the need for surgical biopsy would be beneficial. To overcome these limitations, DSC-MRI evaluation of relative cerebral blood volume (rCBV) has been proposed for response assessment of high-grade gliomas (HGG) and differentiation of tumor recurrence from PTRE. The translation of clinical DSC-MRI across multiple institutions remains challenging due to site-specific acquisition and analysis variability. To improve the repeatability, accuracy and multi-site consistency of DSC- MRI, the National Brain Tumor Society (NBTS) formed an international committee of leading DSC-MRI investigators to standardize DSC-MRI methodology. As members of this committee, we are well positioned to validate the clinical utility of the consensus DSC-MRI protocol across multiple institutions and major MRI vendors. We will leverage our unique expertise in image-recorded stereotactic biopsies to compare clinical performance of the consensus protocol against histologic and clinical benchmarks. Specifically, we first aim to validate rCBV accuracy, as measured by the consensus DSC-MRI protocol at multiple sites and MRI scanner vendors, for differentiating glioblastoma (GBM) recurrence from PTRE. Next, we will determine the repeatability of the consensus DSC-MRI protocol. Finally, we will determine the utility of rCBV measured with the consensus DSC-MRI protocol for predicting overall survival (OS) in GBM patients with recurrent or progressive contrast enhancing lesions. The proposed studies will provide the first multi-site validation of the consensus DSC-MRI protocol and identify rCBV thresholds for differentiating tumor recurrence and PTRE. Such a validation will help to promote widespread adoption of the consensus DSC-MRI protocol, thereby improving the reliability of DSC-MRI for response assessment of HGGs in routine neuro-oncology practice and prospective clinical trials.